Electric discharge device



Oct. 31, 1939. L. J. DAVIES 2,177,690

ELECTRIC DISCHARGE DEVICE Filed July 9, 1957 INVENTOR I Leonard John Dawes Fir M4 wfi AT ORNE E Patented Oct. 31, 1939 PATENT OFFICE 2,177,690 ELECTRIC mscmmcr. DEVICE Leonard J. Davies, Rugby, England, assignor to General Electric Company, a corporation of New York Application July 9, 1937, Serial No. 152,816 In Great Britain July 13. 1936 2 Claims.

This invention relates to electric discharge devices and more particularly to devices in which the discharge takes place in mercury vapor.

It is a characteristic of the electric discharge in mercury vapor that as the pressure of mercury vapor increases the arc becomes constricted and has a cross section less than that of tube or bulb containing it. For example, in a lamp consisting of a tube with an internal diameter of some 4 mms. operating at a current of about .4 a. and having a pressure such that the voltage drop between electrodes approximately 2 cms. apart is 200 v., the luminous arc stream is about 1 mm. in diameter only.

Since this luminous arc stream is a conductor carrying a current and since also it is flexible in that it consists of particles in the gaseous phase, it can be deflected by a magnetic field. If the arc is supplied by alternating current and the applied magnetic field is constant then the arc will move across the tube with a frequency twice that of the supply frequency. If the arc is operated on D. C., then a similar movement can be produced by a magnetic field that is provided by a solenoid operated on A. C. The frequency of movement .of the arc can be varied by varying the frequency of the A. C. magnet.

The are can be made, especially at high mercury vapor pressure, a source of high intrinsic brilliancy, and since it can be moved at high frequency entirely electrically and with an absence of moving mechanism the movement can be used for oscillograph work, measurement of current, signalling devices and for television or other P poses.

Such uses, however, are restricted, by the limited movement normally available in a small diameter tube, or if the tube diameter is made larger to allow for greater movement, by the fact that the shape of the arc is distorted the further it is deflected from the straight line path between the electrodes. This distortion is such that the linear arc becomes bow shaped, since the extremities of the are are fixed by the position of the electrodes, and the arc is extensible.

The object of the present invention is to provide a gaseous electric discharge lamp device so constructed as to secure a large range of movement of an are under the influence of a magnetic field, the are remaining linear in shape. Still further objects and advantages attaching to the device and to its use and operation will be apparent to those skilled in the art from the following particular description.

In practice the lamp is provided with elongated thermionic electrodes arranged in the shape of a truncated V. With such an arrangement the are normally runs from those portions of the electrodes most closely adjacent to each other, as in this position the voltage drop will be a minimum. Under the influence of a magnetic field the arc can be forced to travel up the V and thus a large range of movement with always a substantially straight arc is 10 possible.

In the drawing accompanying and forming part of this specification two embodimentsof the invention are shown, in which Fig. 1 is a side, sectional view of a gaseous electric discharge lamp device embodying the invention,

Fig. 2 is a similar view of another gaseous electric discharge lamp device embodying the invention, and

Fig. 3 is a sectional view of an electrode useful in the embodiments of the invention shown in Figs. land 2.

Like numbers denote like parts in all the figures. I

In Fig. 1, I represents an envelope of quartz or other suitable material containing electrodes 2 and 3 of tungsten or other suitable material. These electrodes are supported on lead-in wires 4 sealed into the envelope l and adapted to be a connected in a suitable circuit. The envelope l contains mercury adapted to be vaporized when the lamp is in operation. When desired the envelope I contains a starting gas, such as argon. As will be seen from the drawing the space between the electrodes 2 and 3 is shaped like an inverted cone or V. The are normally strikes and remains in the position shown in full linesas this is the shortest distance between the electrodes. Under the influence of a magnetic field it is caused to travel up the electrodes to the position shown in dottedlines, when desired, which will be the limit of its travel. Between these two positions the arc will always be substantially straight.

The lamp shown in Fig. 2 is substantially the same as that shown in Fig. 1 except that it is inverted so that the shortest distance between the electrodes is at the top. This is preterable as then convection currents force the are to the shortest path which is the natural path to adopt and stable operation is secured. A ma netic fleld is used to cause the arc to travel down the electrodes 2 and 3, when desired.

Fig. 3 shows a form of electrode which may be adapted. Instead of solid tungsten we may use a sheet of tungsten 5 enclosing a pellet of electron emissive material 6, such as barium oxide. The edges of the tungsten are brought close to- 3 gether as shown but do not touch, a narrow slit being left between them to allow of the emission of electrons.

It may be necessary in order to maintain the arc in a constricted form of high intrinsic brilliancy to heat the arc containing bulb by an external source of heat in order to maintain the pressure.

While I have shown and described and have pointed out inrthe annexed claims certain novel features of the invention, it will be understood that various omissions, substitutions and changes in the forms and details of the device illustrated and in its use and operation may be made by those skilled in the art without departing from the broad spirit and scope of the invention, for example, activating material, such as barium oxide, is applied toor incorporated in the tungsten electrodes 2 and 3, when desired.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A gaseous electric arc discharge lamp device comprising a container, hermionic electrodes sealed therein, a gaseous atmosphere therein, each of said electrodes having an elongated, are discharge supporting surface, said electrodes being mounted in said container in such position relative to each other that the discharge supporting surfaces thereof form a truncated V to permit the movement of the ends of a constricted, linear shaped, luminous arc discharge over said surfaces in response to a magnetic field.

2. An electrode for a gaseous electric are discharge lamp device, said electrode being a foursided hollow metalbody having two parallel sides and a third side at right angles to said parallel sides, sa'id parallel sides and said third side being rectangular, the fourth side of said body consisting of two rectangular parts, each of said parts being at an angle greater than 90 to said parallel sides, the adjacent edges of said parts being separated to form a narrow slit and a pellet of material having high electron emissivity characteristics mounted in said hollow body, the discharge supporting surfaces of said electrode being the outer surfaces of said rectangular parts forming the fourth side of said hollow body.

LEONARD J. DAVIES. 

